Graphical patterns may be used to convey information. A pattern may be printed or otherwise affixed to an item such as a document or an article of manufacture, for example. The pattern can then be used for various control and monitoring functions by using equipment to read the barcode. One such pattern is a barcode, and the most common barcodes are one-dimensional, meaning the barcode pattern varies in only one direction (e.g., the horizontal direction) and are fixed or constant in other dimensions (e.g., the vertical dimension). One-dimensional barcodes are used in applications that do not require a great deal of information to be conveyed by the barcode. An example of such low-information applications is bar coding of consumable and food products sold through food stores. One-dimensional barcodes are rendered by machines, and are read by machines. The (typically) alternating thicker and thinner vertical bars that comprise the one-dimensional barcode are not susceptible to interpretation by a human. That is, a human cannot derive any information by viewing a one-dimensional barcode.
Two-dimensional barcodes are known that can be used to provide more information than one-dimensional barcodes. Two-dimensional barcodes use intricate patterns that vary in both the horizontal and vertical directions. An exemplary two-dimensional barcode system is described in U.S. Pat. Nos. 5,060,980, 5,486,686, and 5,459,307. This system uses bars that are oriented out of the vertical plane e.g., the bars are slanted at 45 degrees from the vertical. The resulting two orientations of the bars allow information to be encoded within the bars.
Visually significant barcodes improve on two-dimensional barcodes by allowing more complex patterns to be encoded within the barcode. However, such visually significant barcodes have a low resolution, making the visually significant barcode coarse and grainy, thereby rendering the visually significant barcode difficult to read by a human. Furthermore, these visually significant barcodes require the original bit map used to generate the barcode in order to decode the visually significant bareode. Thus, current visually significant barcodes cannot be effectively used for many data and document control functions.